Re: [PATCH resend RFC 9/9] s390/mm: optimize reset_guest_reference_bit()

Claudio Imbrenda
2021-09-27T17:02:43Z

On Thu, 9 Sep 2021 18:22:48 +0200
David Hildenbrand <david@redhat.com> wrote:

> We already optimize get_guest_storage_key() to assume that if we don't have
> a PTE table and don't have a huge page mapped that the storage key is 0.
>
> Similarly, optimize reset_guest_reference_bit() to simply do nothing if
> there is no PTE table and no huge page mapped.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
> arch/s390/mm/pgtable.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
> index 534939a3eca5..50ab2fed3397 100644
> --- a/arch/s390/mm/pgtable.c
> +++ b/arch/s390/mm/pgtable.c
> @@ -901,13 +901,23 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr)
> pte_t *ptep;
> int cc = 0;
>
> - if (pmd_lookup(mm, addr, &pmdp))
> + /*
> + * If we don't have a PTE table and if there is no huge page mapped,
> + * the storage key is 0 and there is nothing for us to do.
> + */
> + switch (pmd_lookup(mm, addr, &pmdp)) {
> + case -ENOENT:
> + return 0;
> + case 0:
> + break;
> + default:
> return -EFAULT;
> + }
>
> ptl = pmd_lock(mm, pmdp);
> if (!pmd_present(*pmdp)) {
> spin_unlock(ptl);
> - return -EFAULT;
> + return 0;
> }
>
> if (pmd_large(*pmdp)) {